Thermostatic switches for high temperature operation are well known in the art. These switches are used in various applications, one of the most notable of which is for appliances, such as irons. In an iron, the thermostatic switch is responsive to the heat of the soleplate, upon which it is mounted. The switch cycles on and off to maintain the temperature of the iron within the desired set range.
The switch structure includes spring members to support the respective contacts. A means is provided for engaging one of the spring elements as the temperature of the switch rises to break the contacts and interrupt the current to the electric heating element, such as the element in the soleplate of the iron.
Several attempts have been made in the past to improve the operating characteristics of this type of switch. For example, there have been switches designed for a broader effective adjustment range, such as shown in the Tsai U.S. Pat. No. 2,742,547, issued Apr. 17, 1956. This particular patent utilizes a bimetal assembly for engaging one of the spring elements to open the contacts. Because of the different operating characteristics of the two bimetal elements of the bimetal assembly, the broader range of operation is accomplished.
Other thermostatic switches of this type have attempted to alleviate the problem of temperature overshoot that tends to occur on the initial operating cycles. For example, the U.S. Pat. No. 4,283,701, to Ryckman, issued Aug. 11, 1981, includes a structure for a bimetal assembly to open the contacts sooner than otherwise on the initial cycles to prevent the overshoot. In this particular device, again two bimetal portions are required, one of which is bent back on itself and separated by a temperature isolating slot. While these structures using dual bimetal portions on the bimetal assembly for engaging one of the springs and breaking the contacts have worked to a limited degree, they are generally more expensive and also leave much to be desired in terms of consistency of operation. Furthermore, neither patent addresses the problem of improving the consistency of operation and thus maintaining a more constant temperature by compensating for the size of the weld area between the contacts on each operating cycle. Thus, a need is established for a new, relatively low-cost thermostatic switch providing a structure responsive to the above shortcomings of the prior art.